The present invention relates to chromatography columns and nets for such columns, of the types mentioned in the preambles of the independent claims.
Chromatography columns often contain a net to prevent media from escaping from the end cells which are used for radially distributing the fluid flowing in from a central inlet at one end of the column and for radially collecting the fluid for subsequent outputting from a central outlet at the opposite end of the column. These nets extend across substantially the whole internal diameter of the column. In the prior art the nets have been made of polymer materials and have been attached (with a supporting backing plate if required) to the central inlet resp. central outlet by means of screws or bolts. The screws or bolts are mounted with their heads on the side of the net facing away from the inlet, resp. outlet, and they pass through suitably sized holes in the net and are screwed into suitably threaded axial holes in the wall of the central inlet resp. outlet.
Alternatively nets have been attached by being mounted on a central inlet or outlet tubular port provided with an internal thread and a stop flange positioned on the outside of the port at a distance from the end where the net is to be mounted which is less than the thickness of the net. The net is then positioned against the flange with the end of the port extending into a central opening in the net. The net is held in place by a threaded end piece which has a tubular portion provided with a thread adapted to mate with the thread on the inside of the port, and a flange at one end which pushes the net against the flange on the port when the end piece is screwed up into the port.
A problem with these mounting methods is that once the net is mounted in a chromatography column then access to the end piece or mounting bolts is limited. When it becomes necessary to detach the tubular port from the net, it is necessary to dismantle the column in order to be able to unscrew the end piece or mounting screws from inside the column. This has the disadvantages that it is time consuming and, for reasons of hygiene, it is undesirable to dismantle a column. Alternatively, it is possible necessary to provide a special tool which can be inserted through the tubular port from the end outside the chromatography column and then expanded laterally in order to grip the flange or in some other way become attached to the flange in order to permit the flange and end piece to be rotated. This has the disadvantage that it is difficult for an operator to see the tool when manoeuvring it into place and it is possible for him to inadvertently damage the end piece, net or port while trying to get the tool to grip the end piece.
A further problem is that the heads of the mounting screws, resp. the end pieces, project into the bed media and interfere with the packing of the bed media.
Additionally, in order to prevent unwanted leakage between the central port and the net, the join between the net and a central port is normally provided with sealing means such as O-rings or gaskets. Similarly, at the outer circumference of the net, in order to prevent leakage between the net and the wall of the column or distributor cell, sealing means such as O-rings or gaskets are provided between the net and wall and/or distributor cell. A problem with such an arrangement is that, if the net is made of woven stainless steel, or sintered metal, it is very difficult to obtain a good seal, as the net surface is uneven and the O-ring or gasket cannot deform sufficiently to fill all the irregularities in the surface of the net. This is particularly problematic if the bed particles used in the column are less than 30 micrometers in diameter or length as they are able to pass through gaps between the O-ring or gasket and the net. This leads to a loss of bed media through these gaps and a loss of column performance.
According to the present invention, at least some of the problems with the prior art are solved by means of a device having the features present in the characterising part of the independent claims. Further advantages are obtained by the features mentioned in the dependent claims. The present invention will be illustrated below by means of descriptions of non-limiting examples of embodiments and the following figures.